The present disclosure relates generally to peel plies for surface preparation of composite substrates, more particularly, resin-based composite substrates, prior to bonding.
Hand sanding, grit blasting and peel ply removal are conventional methods for preparing surfaces of resin-based composite substrates for adhesive bonding in aerospace industry. Adhesive bonding by peel ply removal is the most common out of the three techniques because it saves significant amount of labor and creates more evenly treated surface. Peel ply removal usually involves applying a dry, textured fabric material onto the bonding surface of the resin-based composite substrate followed by curing. After curing, the peel ply is removed, i.e. peeled off, to reveal a roughened or textured bonding surface. However, dry peel plies tend to leave residual broken fibers on the bonding surface after peeling. This leads to poor adhesive bonding properties because the residual fibers can act as defects that prevent the adhesive from completely wetting the bonding surface of the composite substrate, thereby resulting in adhesive failure. The general industry experience has been that the peel ply process lacks reliability and predictability with regard to bonding performance.